Geology Across America

Download 24.7 Kb.
Size24.7 Kb.

Geology Across America

1. Geology of the Appalachian Mountains:

These mountains extend from Maine to Alabama with the highest elevation sitting at Mount Mitchell in North Carolina (over 6000 feet). Historical interest concerning these mountains is the Appalachian Trail, which follows the crest of the mountain chain and can be hiked from Maine to Alabama. Settlers migrated from Pennsylvania along the mountain crest to populate the lower states.
These mountains are a thick sequence of Paleozoic Sediments that were extensively folded with the Valley and Ridge regions of Pennsylvania to be excellent places for us to examine the creation of anticlines and synclines from the pressures created by the collision of the North American Plate with the African plate and European plate, as evidenced by the Caledonians in Scotland. (There is controversy over the breadth of the impact of this place activity.)
The first location of extracted petroleum in the US was in Titusville, Pa., back in the 1830’s. The extensive sequences of folding in the eastern part of these mountains in Pennsylvania resulted in Pennsylvanian and Mississippian Paleozoic coal beds to undergo metamorphism. This is the source of the rich anthracite coal reserves of Pennsylvania.
As we examine the mountains and the regions to the left and right, we note that there are few Mesozoic and little Permian (Paleozoic) sediments preserved. Part of this could be from erosion, but is linked with the mountain building that created the mountains. As they were being uplifted, sediments would be deposited on the flanks. There are some Triassic basins in North Carolina, but there is also evidence of igneous intrusions in New York, The Palisades Sill, that is Triassic in age. In general, if you want to find Mesozoic aged sediments, you will need to go to the western states. This is one reason there are few fossil remains of dinosaurs in the Appalachians. Mesozoic (age of the dinosaurs) sediments are not available in thick sequences in the eastern part of the United States.
2. The Atlantic Coast
We discussed the passive margin of the Atlantic Coast and compared it with the active margin of the west coast. Looking at the geologic map of the US, we see that the continental shelf extends well beyond the shoreline. There is a long shore current that flows from south to north that is driven by the warm currents of the Gulf Stream, which originates in the warm waters of the Caribbean. There is a cold current that flows to the south and hugs the shoreline from Labrador (NE Canada) down past the outer banks of North Carolina. In North Carolina alone, there is over 200 miles of National Shore, preserved for prosperity.
The passive margin allows for the build up of sediments that are poured heavily onto the continental shelf by numerous streams that flow off the eastern flanks of the Appalachians into the Atlantic Ocean. A combination of the sediment load and the flowing currents have allowed movement of sands with the long shore current to help form the barrier islands. (There are barrier islands along the Gulf Coast too.)

Another interesting thing about the east coast is that the area around Chesapeake Bay down to North Carolina which are areas of subsidence. This allows some of these low-lying, tidewater areas, to be in a slow state of drowning.

Impact craters created Chesapeake Bay, Hudson Bay and the Yucatan depressions. More work is being done on this, but the finding of Yttrium and Iridium layers in the Cretaceous sediments, at the Mesozoic and Cenozoic boundaries have been traced to the extinction of the dinosaurs and the proliferation of the mammals.
3. Florida
Florida is an old reef. Well, the Key Islands are part of an old reef track that was slightly uplifted. The current reef track is just to the east of the Florida Keys lying in water just deep enough to allow the corals to grow. As we examine the state, there are extensive karst lakes that formed from surface and subterranean waters flowing through the old reef rock and eroding it. Many regions in Florida have problems with homes, business and cars falling into a collapsing sinkhole.
The Ocala Uplift formed a dome in the central region of the state. All rivers to the south of the dome flow to the south. Those to the north flow to the north. The St. John’s River is a fairly large river that originates from waters running to the south, off the Ocala Uplift. This is the only good-sized river in the United States that flows south to north. It empties into the Atlantic at Jacksonville.
Because of the reef rock and the subsequent elevation caused by the Ocala Uplift, Florida has Phosphate as one of its mineral resources. Most of this is used to make fertilizer. Apatite is a phosphate mineral that is found there. They believe that trapped fishes in these pockets of reef rock eventually died and the pool dried up, supplying the organic material needed to create the phosphate deposits.
4. The Great Lakes

The 5 Great Lakes, HOMES, Huron, Ontario, Michigan, Erie and Superior, are glacial features, remnants of the Pleistocene Glaciation. The lakes flow from west to east, into the St. Lawrence Seaway and into the Atlantic Ocean. For traffic to travel from Lake Erie to Lake Ontario, a system of locks had to be built. The reason for this is that the several-hundred foot drop created by Erie forming the Niagara River, and it flowing over Niagara Falls eventually making its way into Lake Ontario. The lock system was dug away from the falls, mostly on the Canadian side. Without it, ships could not travel from Superior to the Atlantic.

The presence of Niagara Falls is due to the Deep Kill Fault’s placement and the erosion of the Deep Kill Shale. This helped to create the vertical displacement between Erie and Ontario. Fortunately, earthquake activity energy that is associated with the Deep Kill Fault seems to be systematically released by nature! From Toronto to Montreal, all along the St. Lawrence Seaway, numerous small earthquakes occur annually releasing energy slowly. Otherwise, Toronto, Buffalo, Cleveland and even New York City could experience devastating earthquakes. They could despite these subtle energy releases. The Deep Kill Fault has a vertical displacement of 1700 feet and is the greatest offset or “largest” fault in North America. The mechanisms that formed this fault probably created the St. Lawrence Seaway and the Hudson River Valley.
All through the Great Lakes area are Silurian reefs. The earthquake that happened in Maysville, Kentucky in 1980 that reached around 5 on the Richter Scale, was attributed to part of a subterranean reef collapsing. Part of this could be related to the extraction of oil from these Silurian limestones. Once the oil was removed, the rock was no longer strong enough to support the surface.

From eastern Kentucky, to Michigan, Indiana, Illinois and Ohio, there are numerous oil wells that extract oil form these Silurian rocks. The source for the oil is linked to the thick Albany or Devonian Black Shale. It was a deep ocean, fine grained, sedimentary deposit that is believed to contain enough oceanic organics to have allowed oil to form, then migrate upward in to the Silurian Reef rock.

The UP, or Upper Peninsula of Michigan contains rich iron beds that was part of the reason that the steel industry grew so quickly in the 1800’s along the Great Lakes. There was coal, to form the coke; water for the industry to run large furnaces; and fairly inexpensive mode of transportation, by lake, to transport iron ore to these foundries.
Eastern states that have coal or oil resources are Pennsylvania, New York, West Virginia, Virginia, Kentucky, Indiana, Illinois, Michigan, and Ohio. Alabama had some minor coal beds and iron deposits which allowed this state to make arms during the Civil War.

5. The Midwest, the Mississippi and Missing Rocks

The Midwestern part of the US has most of its rocks covered in thick sediments. There are few natural outcrops. The Mississippi and other rivers are attributed with pouring thick layers of sediments from the Rockies to the West and the Appalachians to the East. The Mississippi River starts in Minnesota and courses through the middle of the country. In the upper part of its channel, the river is narrow and doesn’t broaden until it passes Cairo, Ill.

When the upper Midwest experienced extensive rains in the summer of 1993, the narrow channel of the Mississippi could not handle the waters to the north. Despite the flooding, once the river reached Cairo, the confluence with the Ohio River, the channel broadened and the lower Mississippi River Valley could handle the great influx of water into its local system. The upper Mississippi River Valley had Rivers from Wisconsin, Minnesota, Iowa, Illinois, and Missouri dumping its usual heavy load of water and sediments into the system, accompanied by heavy rains where streams and creeks backed up, causing dry creeks in subdivisions to fill where they never had sustained a constant flow of water before.

There are thick sequences of sediment overlying the Paleozoic sedimentary rocks that underlie the Mississippi River Valley. The Curdsville Limestone in Kentucky is Middle Ordovician in age. In Illinois it is several hundred feet below the surface, where it is found in outcrops in several counties surrounding Lexington, Kentucky.
6. The Mississippi Embayment

This feature can be viewed on the geologic map of the US as a v-shape or delta shape. This is because the Mississippi River is has a pro-grading delta that has spread thick sediment layers all through the midsection of the country. The lower portion of the Mississippi River has a thick sequence of sediments that have built up and migrated toward the Gulf of Mexico.

As we look at the land we will see numerous meanders, meander scars, oxbow lakes and yazoo rivers. This is a meandering river that runs parallel to another major, meandering river. In the state of Mississippi, there is a river named the Yazoo River for when this term was derived.

Moving southward into Louisiana, salt domes preserved in the deep sediments hundreds to thousands of feed down. These domes are very plastic and will deform from the overlying sediments. Also, there are oil and natural gas fields that lie in Mississippi, Louisiana, Texas and the Gulf of Mexico. If you go to Galveston Beach on a clear day and look into the Gulf of Mexico, you can see oil-drilling platforms 7 to 10 miles out to sea.

The Mississippi Delta is still pro-grading, or moving into the ocean. As these sediments are dumped into the ocean, they slowly build up. This area is in a state of subsidence and will continue to slowly sink downward as sediments are poured on top of sediments, building shallow areas with the delta front moving into the sea.
7. The Black Hills and Badlands of South Dakota

Gold was found in the Black Hills in the 1850’s. It is still mined there today and specifically sold as Black Hills Gold Jewelry. This area has a old sequence of Paleozoic and Pre-Cambrian Rocks that have been metamorphosed and affected by volcanism.

Also in South Dakota we find the Badlands, with is a dry area with extensive weathered clays and shales that form extensive mazes. It was called the Badlands because only those running from the law were brave or desperate enough to wander into Hostile Indian territory that had no water, no food and was difficult to navigate through.
8. The Rocky Mountains

The major mountain chain of the contiguous US and Canada started forming in the late Cretaceous to early Tertiary, during the extensive Cordilleran Orogeny, thick sequences of Paleozoic and Mesozoic sediments were uplifted and folded. The highest part of the mountains sit in Canada, and the southern end, also know as the Sangre de Cristo Mountains Northern Mexico, still reach to 13,000 feet.

Throughout the Rocky Mountains, we have separate ranges, like those in New Mexico, those outside of Denver, and even the Grand Teton Mountains in Wyoming. They have experienced extensive thrust faults, listic faults, and tilting of large blocks of sedimentary rock to form one of the world’s larges mountain ranges.

9. Montana, Idaho and Washington and the Columbian Plateau

Looking west of the Rockies and east of the Cascade Mountain Range, we find the Columbian Plateau. This is an area of extensive basalt flows that still experience regional earthquakes. Traveling large areas we find miles and miles of lava flows. Part of this may be due to the hot-spot that Yellowstone is currently experiencing.

For thousands of years, slowly oozing basalt flows poured over the landscape to create the Columbia Plateau, in which the Columbia River dissects and moves into Washington State where the Grand Coulee Dame is found.

10. The Basin and Range of the West

We see extensive faulting and lava flows during the Tertiary. From 30 to 15 million years ago, southern New Mexico, Arizona, California, Nevada and northward, we find that tension pulled great sections of sedimentary rock overlying Pre-Cambrian basement rock apart, both rock types broke along the normal fault planes with the up-block being left as a mountain range, and the down-thrown block as a basin. Nevada contains the greatest majority of the Great Basin, and Phoenix and southern parts of Arizona lie in the lower rim of the Basin and Range.

Thick sequences of sedimentary Paleozoic rock were eroded from the Transition Zone in the middle of Arizona, southward. The eastern edge of California experienced this pull-apart energy and we can readily find volcanoes and lava flows throughout these areas.

The mountain ranges originally existed as angular blocks. Some were twisted or rotated, but all have been eroded. Thick sediments and poured into these basins. Here, in the western edge of the Phoenix Valley, we find the Luke Basin, that has 9000 feet of sediments that overlie 1700 MA gneiss and schists and granites.

11. The Sierra Nevada Batholith, the Cascades and the San Andreas Fault.

The Sierra Nevada Batholith includes Yosemite. This extensive granitic batholith is what forms the Sierra Nevada Mountains. They are believed to have formed from the pushing of the Pacific and North American Plates against one another. In Northern California, Oregon and Washington, we see the Cascade Mountain Range that formed from the pushing of the Juan de Fuca plate underneath this area, forming this volcanic mountain chain, of which Mount St. Helens and Mt. Rainier are notable volcanoes.

As the batholith formed and the San Andreas ripped open the Gulf of California and tore across the southwestern edge of California, extensive igneous material moved upward, and extensive faulting occurred. In general, the meeting of these plates has caused the west coast to move upward and become an active margin.

In places around San Francisco, we see oceanic sedimentary rock pushed up onto the land, cliffs that over look the Pacific Ocean, and an area which experiences hundreds of earthquakes annually. As the coast moves upward (the North American Plate’s western edge moves upward) the Juan de Fuca is ground under the continent as the San Andreas allows the plates to gradually grind past one another.

Coldwater, deep sea currents move quickly southward and cuts and erodes the coast rapidly. Both the currents, the lack of a broad continental shelf, and constant uplift and earthquakes, prevents the west coast from having barrier islands form.

Download 24.7 Kb.

Share with your friends:

The database is protected by copyright © 2022
send message

    Main page